1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus having a high recording density. The invention further relates to a magnetic head allowed to stably provide such a magnetic recording and reproducing apparatus as described, and more particularly relates to a magnetic head having a reproducing head with a magnetoresistive layer arranged between a pair of magnetic shield layers.
2. Related Arts
The magnetic recording and reproducing apparatus such as a magnetic disk device comprises a medium for magnetically recording information; a magnetic head provided with a recording element and a reproducing element for recording or reproducing information on the medium; a recording and reproducing operation control circuit for reproducing information on the basis of an output signal from the magnetic head and recording information on the basis of a signal input; a mechanism for rotating or moving the medium; and a positioning mechanism for deciding a position of the recording and reproducing head relative to the medium.
A recording element constituting the magnetic head comprises a coil for generating magnetic flux; a pair of magnetic cores for collecting magnetic flux; and a recording gap arranged between a pair of magnetic cores for generating a magnetic field. The magnetic cores generally used include an alloy layer of nickel and iron such as Ni80Fe20 and Fe55Ni45, an alloy layer of cobalt base, or a layer having about two layers of them laminated. The thickness of each core is often set to 1 to 4 xcexcm. The recording operation is performed by applying a magnetic field generated by conducting a recording current to the coil onto the medium.
A reproducing element constituting the magnetic head comprises a pair of magnetic shield layers, a magnetoresistive layer between the pair of magnetic shield layers and arranged spaced apart by a predetermined distance from each shield layer, and a pair of electrodes connected electrically to the magnetoresistive layer. The magnetoresistive layer can be classified roughly into an AMR layer (anisotropic magnetoresistive layer) utilizing the anisotropic magnetoresistance, and a GMR layer (giant mageto-resistive layer) utilizing the giant magnetoresistance. The AMR layer is composed of, for example, a Ni80Fe20 layer having a thickness ranging from from 5 to 30 nm or the like. The GMR layer is composed of a laminate layer comprising a first ferromagnetic layer having a thickness of approximately 2 to 10 nm of which magnetization direction is changed by a magnetic field leaking from the medium, a second ferromagnetic layer having a thickness of approximately 1 to 5 nm of which the magnetization direction is almost fixed, and a non-magnetic conductive layer whose thickness is approximately 1 to 4 nm inserted between the first ferromagnetic layer and the second ferromagnetic layer. The GMR layer can obtain a higher output even by a small magnetic field compared with the AMR layer. That is, since the GMR layer is more sensitive, it is advantageous for a higher recording density of the magnetic disk device. In the magnetic disk device, a change in electro-resistance of these magnetoresistive layers is detected as an output signal by applying a detecting current. A pair of magnetic shield layers are provided for detecting a change in magnetic field leaking from the medium with high resolution. Since the narrower the spacing between the pair of shield layers, the higher resolution is obtained. Therefore the spacing between the shields is being narrowed corresponding to the future higher recording density of the magnetic recording and playback apparatus. In addition, the magnetic shield layer has a function to release, outside, heat generated in the magnetoresistive layer by applying a detecting current. As the magnetic shield layer, an Ni80Fe20 layer, and an alloy layer with the former being a base are often used. Further, as the shield layer (lower shield layer) on the substrate side, sendust (Fexe2x80x94Alxe2x80x94Si) and an alloy layer such as the amorphous of a cobalt base are sometimes used, in addition to those mentioned above. A thickness of each shield layer is generally set to 1 to 4 xcexcm in thickness.
Where a magnetic head with the recording element and the reproducing element formed on the same substrate is used, one of the pare of magnetic cores of the recording element in the side near the reproducing element, that is, the lower core is also used as the upper shield layer of the reproducing element, in order to reduce a displaced width between a position of the write gap and a position of the masgnetoresistive layer. In case of a magnetic head in which the recording element and the reproducing element combined are unified, there is a case of employing a constitution in which for the purpose of suppressing noises during the reproducing operation, one non-magnetic layer such as alumina having a submicron thickness is inserted into the upper shield layer, and a ferromagnetic metal layer having 1 to a few xcexcm in thickness, a non-magnetic layer having a submicron thickness, and a ferromagnetic metal layer having a thickness of 1 to a few xcexcm are laminated sequentially.
Generally, the magnetic core of the recording element and the magnetic shield layer of the reproducing element are formed using a metal layer as a main component in any case. In this case, when the spacing of the shields is narrowed to cope with the higher density of the magnetic disk device, insulation between one or both shield layers and the magnetoreistive layer or an electrode connected to the magnetoresistive layer is often damaged due to electrostatic discharges or the like to increase a probability in which a considerable reduction in reproducing signal amplitude (the amplitude is often substantially zero) and an increase in noises occur, resulting in an erroneous operation of the magnetic disk device and the lowering of yield of the magnetic heads. The damage to the magnetic heads caused by electrostatic discharges is not limited to only the time when the magnetic heads are being fabricated. It is well known that for example, in the process in which a person comes in contact with the magnetic heads such as the work of incorporating the magnetic heads into the magnetic disk device, if the control of electrostatic discharge is not sufficient, there is the possibility of giving the damage to the magnetic heads. Further, even after the magnetic heads have been incorporated into the magnetic disk device, for example, when a charged-up person or the like comes in contact with a casing (often, an electric ground) of the magnetic disk device, a ground potential is varied to generate a potential difference in the magnetic heads, thus giving damages.
The electrostatic discharge damage to which the head is subjected can be considered roughly based on causes as follows. A first case is the case where an abnormal voltage is applied due to electrostatic discharge between a pair of electrodes connected to the magnetoresistive layer, in which case, the magnetoresistive layer is sometimes broken or fused due to heat generated by a current. A second case is the case where an abnormal voltage is applied due to electrostatic discharge between one or both of shield layers arranged with a magnetoresistive layer sandwiched and the magnetoresistive layer or an electrode(s) connected to the magnetoresistive layer, in which case, the magnetoresistive layer is sometimes broken or fused by discharge which occurs between the shield layers and the magnetoresistive layer or the electrode(s), and the shield layers and the magnetoresistive layer sometimes become short-circuited.
In any case, the magnetic head is not operated normally any longer. In particular, where the spacing of the shields is made narrower than 100 nm, the probability of giving the damage due to the discharge which occurs between the shield layers and the magnetoresistive layer or the electrodes increases rapidly. Therefore, settlement of this problem has been desired in view of the stable operation of the magnetic disk device and the enhancement of the yield of the magnetic heads.
As one method for solving the problem, for example, Japanese Patent Laid-Open No. 5-266437 proposes that an insulating magnetic layer (NiZn ferrite material is illustrated) is arranged on the surface of at least one magnetic shield layer on the magnetoresistive layer.
It is known that with respect to a magnetic thin film having a high electrical resistivity, for example, Coxe2x80x94Alxe2x80x94O and Fexe2x80x94Sixe2x80x94O have a high electrical resistivity ranging from 10 to 105 xcexcxcexa9xc2x7m.
Further, Japanese Patent Application Laid-Open No. 11-86234 which corresponds to copending U.S. application Ser. No. 09/116,526, filed Jul. 16, 1998, or Japanese Patent Laid-Open No. 8-147634 describes that a continuous laminate layer of a ferromagnetic metal layer and an insulting material layer is used as a magnetic shield layer, or a layer of a ferromagnetic metal layer and an insulating compound layer is used.
It is therefore an object of the present invention to provide a recording and reproducing apparatus having a high stability, in which even where a space of shields is narrowed for higher recording density of a magnetic recording and reproducing apparatus, deterioration in characteristic caused by short-circuiting between a magnetoresistive layer and a magnetic shield layers is prevented, the magnetic recording and reproducing apparatus being reduced in erroneous operation.
It is a further object of the present invention to provide a high output magnetic head with high yield, without carrying out high temperature heat treatment, and to realize a magnetic recording and reproducing apparatus of high recording density.
For achieving the aforementioned objects, there is provided a magnetic head comprising a pair of magnetic shield layers, a magnetoresistive layer arranged between the pair of magnetic shield layers, and a pair of electrodes electrically connected to the magnetoresistive layer, at least one of the pair of magnetic shield layers comprising a discontinuous multi-layer formed by alternately laminating a plurality of ferromagnetic metal layers and a plurality of insulating material layers.
The discontinuous multi-layer constituting the magnetic shield layer can be optimized and thereby set so as to have sufficient permeability as a magnetic shield and electrically sufficient resistivity.
FIG. 11 shows a wave-form indicating of a relationship between distance x from the center between a pair of magnetic shields and magnetic field Hy in the case where permeability of a magnetic shield layer is changed as in 10, 100, 500. When the permeability of the magnetic shield layer is 10, the waveform is spread, and the shield effect is small. It is found that where the permeability of the magnetic shield layer is than 100 or more, the sufficient shield effect is obtained.
That is, since the width of the reproduced wave-form is kept narrow, the permeability is preferably 100 or more, desirably, not less than 500.
With respect to the electrical resistivity, the ratio between a current flowing through a GMR layer and a current flowing through a magnetic shield layer is determined by the ratio between the electrical resistivity of the GMR layer and the electrical resistivity of the magnetic shield layer. With respect to the GMR layer, normally, the sum total of thicknesses of first and second ferromagnetic layers and a non-magnetic conductive layer affecting on the reproducing output is approximately 10 nm, a height (a) of an element (width depthwise from an air bearing surface) of the GMR layer is 0.2 xcexcm, and a track width (b) is 0.3 xcexcm. With respect to the magnetic shield layer, a thickness of the magnetic shield layer is 100 nm, a height of the magnetic shield layer in which part a current flows is about 10 times (2 xcexcm) of the height (a) of an element of the GMR layer, and a width thereof is (0.3 xcexcm) equal to a track width (b) of the GMR layer. From the foregoing, the volume ratio of GMR layer:shield is 1:100 (10xc3x97axc3x97b:100xc3x9710axc3x97b). It is generally desired that even where insulation between the magnetic shield layer and the magnetoresistive layer or an electrode is broken, a current flowing through the magnetic shield layer be not more than {fraction (1/10)} of a current flowing through the magnetoresistive layer in order to prevent a detecting current from shunting to the magnetic shield layer. Accordingly, for making a current flowing through the magnetic shield layer having the volume 100 times of the GMR layer not more than {fraction (1/10)}, the electrical resistivity of the magnetic shield layer should be made not less than 1000 times of that of the GMR layer. Therefore, the electrical resistivity of the magnetic shield layer is desired to be approximately 0.1 mxcexa9xc2x7m which is 1000 times of that of the magnetoresistive layer (approximately 0.2 xcexcxcexa9xc2x7m to 0.3 xcexcxcexa9xc2x7m) or more.
The discontinuous multi-layer sometimes has the aforementioned good characteristic by setting a thickness of each layer of the ferromagnetic metal layer and the insulating material layer to approximately 0.5 to 5 nm, though being different depending on the layer forming conditions. As shown in FIG. 2A, a thickness 611 of a ferromagnetic metal layer 61 is made to be not more than 5 nm whereby the ferromagnetic metal layer constitutes no continuous layer evenly spread in the direction of in-plane but is in the form of islands, and an insulating material 62 is formed so as to bury therebetween. As a result, a discontinuous multi-layer, in which each layer of both the ferromagnetic metal layer 61 and the insulating material layer 62 is discontinuous with keeping both layer in two-dimensional arrangement (layer structure) in a plane, can be obtained. By employing this structure, a layer being suitable for magnetic shield, which has high resistivity of 0.1 mxcexa9xc2x7m or more and keeps good permeability of 100 or more, is realized. On the other hand, by setting the thickness of ferromagnetic metal layer too thin, islands which is formed become small and it become difficult to magnetize the layer for external magnetic field by demagnetizing field, that is, its permeability become lower. In order to prevent this, the thickness of the ferromagnetic metal layer 611 is desired to be about 0.5 nm or more. When the thickness of the insulating layer 621 is thick, a ratio of ferromagnetic metal layer becomes low in the whole multi-layer and the amount of saturation magnetization amount becomes low. As a result, its permeability becomes low. By setting the thickness of insulating material layer too thin, ferromagnetic metal layer 61 is not separated sufficiently and its resistivity becomes lower. The thickness of insulating material layer 621 is desired to be 0.5 nm to about 5 nm to get sufficient permeability and resistivity. The most biggest difference between a continuous multi-layer and a discontinuous multi-layer is in its resistivity. In case of a continuous layer including thick ferromagnetic metal layer, the resistivity is in range of from 0.1 xcexcxcexa9xc2x7m to about 1 xcexcxcexa9xc2x7m which is nearly order of resistivity of its bulk material, or to at most 200 jxcexa9xc2x7m (0.002 mxcexa9xc2x7.m) which is shown in Japanese Patent Application Laid-Open No. 11-86234 or Japanese Patent Application Laid-Open No.8-147634. However high value of resistivity, which is beyond comparison as compared with a continuous multi-layer being 0.1 mxcexa9xc2x7m, can be obtained. Therefore, in view of resistivity, a discontinuous multi-layer is required in stead of a continuous multi-layer.
It is in need of low temperature process in which the temperature is in range of about 250xc2x0 C. or less for forming a discontinuous multi-layer, in order to obtain a discontinuous multi-layer in which each layer of both the ferromagnetic metal layer 61 and the insulating material layer 62 is discontinuous with keeping both layer in two-dimensional arrangement(layer structure) in a plane. Because high temperature process in which a temperature is in such as 300xc2x0 C. or more, causes disarrangement of each layer of both the ferromagnetic metal layer 61 and the insulating material layer 62. Therefore, in case of using a magnetic shield layer having a discontinuous multi-layer, thermal deterioration of GMR layer could be avoided, because it is no need to employ high temperature treatment in a manufacturing process. As a result, a magnetic recording and reproducing head having narrow spacing of shields and high output could constantly be obtained.
A mixed layer of ferromagnetic metal and insulating material can be also used as a magnetic shield. In case of employing the mixed layer, degree of freedom for combining ferromagnetic metal with insulating material is restricted as compared with a discontinuous multi-layer, because there is a trade-off relationship between resisitivity and permeability, that is, large amount of ferromagnetic metal causes increasing apermeability and decreasing a resisitibility, and on the other hand, large amount of insulating material causes increasing a resisitivity and decreasing a permeability.
It is useful to using a discontinuous multi-layer in order to get predetermined permeability and predetermined resisitibility.
In case of using a mixed layer as a magnetic shield layer, the above-said good characteristic can be obtained by setting the ratio of ferromagnetic metal and insulating material in range of from 1:2 to about 3:1. The mixed layer is a layer in condition of mixing of ferromagnetic metal and insulating material in three dimension, and of that both of ferromagnetic metal and insulating material are in a form of particle or ferromagnetic metal in a form of particle encloses insulating material, so that the mixed layer has a structure in which these particles are separated each other. In case of large content of ferromagnetic metal, particles of ferromagnetic metal are not fully separated, so that resistivity of this layer becomes low. In case of low content for ferromagnetic metal, amount of saturation magnetization becomes low, so that permeability of this layer becomes low. The above-said ratio of ferromagnetic metal and insulating material is preferable to satisfy both characteristics of resistivity of about 0.1 mxcexa9xc2x7m and permeability of 100 or more.
In case of employing a discontinuous multi-layer in which a plurality of the above-said ferromagnetic metal layers and a plurality of the above-said insulating material layers are formed by laminating alternately, or a mixed layer of ferromagnetic metal and insulating material as a magnetic shield, it is preferable to employ layers as both of a lower shield layer being near a substrate and upper shield layer being near a recording element. However, of course, it can be used on only one side. In this case, it is preferable to employ the above-said shield layer as a shield layer being in contact with more thinner gap layer selected from a lower gap layer inserted between a magnetoresistive layer and a lower shield layer and an upper gap layer inserted between magnetoresistive layer and an upper shield layer. A gap layer often formed by insulating material, for example alumina or silicon oxide, because a thin gap layer has a higher possibility of breaking insulation than a thick gap layer. When thicknesses of both gap layers of upper and lower are approximately equal, it is preferable to apply the above-said shield layer to a shield layer on which an electrode is formed(it is often upper shield layer). Because thickness of a gap layer being between an electrode and a shield layer often thin, so that insulation is easily destroyed on this gap layer. Nickel based alloy can be also employed as ferromagnetic metal contained in the magnetic shield layer. Because it is difficult to make amount of saturation magnetization of Nickel based alloy in the same level of Cobalt based alloy or Iron based alloy, however it is comparatively easily to suppress coercivity low, so that high permeability can be obtained. Ni80Fe20 can be given as a main example. Amount of saturation magnetization of this alloy is about 1.0 Tesla, but coercivity is about 100 A/m and is sufficient low. And it is useful to that magnetostriction can be also suppressed sufficient low, that is in about 1xc3x9710xe2x88x927.
Insulation material contained in a magnetic shield layer can be used by selecting at least one element from a group of oxide, nitride, carbide, boride of Alumina or silicon, and boron nitride and by combining the above-said elements.
By selecting the above-said ferromagnetic metal and insulating material, high temperature treatment of over 300xc2x0 C. in a process of forming a mixed layer is not needed. When forming a mixed layer, ferromagnetic metal or insulating material which do not require high temperature treatment have to be selected, because of preventing destroying magnetoresistive layer.
Therefore, high temperature treatment of over 300xc2x0 C. in a process of forming a magnetic shield layer is not needed, so that GMR layer which is weak for in high temperature process but is high sensitive can be employed as a magnetoresistive layer.
Moreover, laminating thin layers of ferromagnetic metal and insulating material layer several times can be used to form a magnetic shield layer of several xcexcm thickness, but this process is not always easily in industry. However making stacked numbers of a multi-layer smaller causes making a thickness of a magnetic shield layer thinner, so that efficiency of radiation of heat becomes low. In this case, combining a magnetic shield layer with another thick heat radiation layer is useful to stack layers, wherein the magnetic shield layer is comparatively thin, that is, by using ferromagnetic metal layer and insulation material layer, the magnetic shield layer is formed in small numbers of laminating layers. Moreover, in case of using mixed layer as a magnetic shield layer, stacking the magnetic shield layer and another heat radiation layer is useful to make an efficiency of radiation of heat higher.
Some materials having high heat conductivity(metal, semiconductor material) can be used as a heat radiation layer, and it is preferable to use soft magnetic metal which is usually used as a magnetic shield layer so far and to set thickness in range of from 1 xcexcm to about several xcexcm. For example, Ni80Fe20 layer, alloy layer which is based thereon, or sendust (Fexe2x80x94Alxe2x80x94Si) and cobalt based amorphous material can be given as the above-said materials having high heat conductivity. Because when uniform and large external magnetic field is applied on a head, a thick heat radiation layer formed by a soft magnetic metal also is magnetized, (because magnetic flux flows into this layer), so that ,it is possible to prevent a relatively thin magnetic shield layer from being magnetically saturated. When a radiating layer is formed of metal, an insulating layer having a predetermined thickness can be inserted in order to prevent an electrical short-circuiting between the magnetic shield layer and the radiating layer. The thinner the thickness, the higher radiating efficiency is obtained, but the insulating property lowers. Preferably, the thickness is set so as to fulfill both of these, 10 to 500 nm.
Ferromagnetic metal contained in the magnetic shield layer can be an alloy of cobalt base or an alloy of iron base, because use is made of the alloy of cobalt base or the alloy of iron base having a high saturation magnetization amount to enhance the permeability of the shield layer. The aforesaid alloys can include nickel or copper in order to lower the coercivity force of the magnetic shield layer. As an influential example, there can be mentioned Co90Fe10. The saturation magnetization amount is as large as approximately 1.8 tesla, and the coercivity is as low as approximately several hundreds of A/m. When the magnetostriction of the shield layer is large, there sometimes occurs a problem of instability such as fluctuation of the reproducing wave-form when a head is constituted. However, since the magnetostriction can be suppressed to be as low as 10xe2x88x927 for such a case, which is advantageous.